1. Field of the Invention
The present invention relates to a vehicle heating system, and more specifically, to a vehicle heating system with coolant-heating device.
2. Description of the Related Art
For the purpose of securing heating performance in vehicles including hybrid vehicles, idling-stop vehicles, etc., vehicle heating systems have been developed, which have a heating device, such as an electric heater, for heating the coolant to be introduced into a heater core.
These vehicle heating systems are equipped with a heating device and an electric pump in a coolant circuit running through the engine and the heater core so that heating may be carried out during engine shutdown. For a quick heating performance during the engine's cold state, some of these systems are further equipped with a four-way valve for switching coolant routes to prevent the coolant circulating the heater core from entering the engine. The four-way valve is actuated by a control unit and is switched on or off according to room or outside temperature (Unexamined Japanese Patent Application No. 2000-108645).
The four-way valve mentioned in the publication, however, is of an electric type like an electromagnetic valve or a motor-operated switching valve, which is relatively expensive. On top of that, the actuation of the four-way valve requires a control unit and a temperature sensor, and thus overall increases the cost of the heating system. Furthermore, since the four-way valve is designed to switch the coolant routes according to room or outside temperature detected by the temperature sensor, it is difficult to properly grasp engine temperature and reflect the engine temperature to the heating control. For instance, when the room temperature is low, the valve is switched to the route that does not lead the coolant circulating the heater core into the engine. In this case, once the room temperature is increased with a quick heating effect, the coolant circulating the heater core is switched to the route running to the engine side. At this point, if the engine is in a cold state, there is the possibility of loss of heating performance as the coolant refrigerated in the engine circulates into the heater core.